1. Field of the Invention
The present invention relates to a semiconductor optical device applied to a technical field such as an optical communication device, a surface emitting laser or the like and, more specifically, to a method for fabricating a semiconductor optical device that can be used as a semiconductor reflector or an optical filter.
2. Description of the Related Art
Semiconductor optical devices have been applied to a variety of fields because of its simple high-density integration and long life span. The semiconductor optical device having a wavelength region for communication (i.e., 1.2 μm to 1.8 μm) is mostly formed on an InP or GaAs substrate. It is possible to obtain the semiconductor optical device that is available for a reflector or an optical filter, in case where materials each having high and low refractive indexes are alternately stacked by each proper thickness. The aforementioned semiconductor reflector or optical filter may be applied to active and passive semiconductor devices. In particular, a highly reflective reflector would be required for implementing a surface emitting laser, and thus various techniques have been applied thereto.
A semiconductor reflector according to a prior art includes an InP/InAlAs reflector, an InAlGaAs/InAlAs reflector, an InAlGaAsSb/InAlAsSb reflector, and the like, which are obtained by lattice-matched growth on an InP substrate [References 1, 5 and 6]. An InP/air-gap reflector has been developed, which can be obtained by lattice matched growth on an InP substrate and selective etch [References 3, 4, 7 and 11]. A dielectric reflector obtained by a deposition method [Reference 2], an Al(Ga)As/GaAs reflector grown on a GaAs substrate [Reference 12], a reflector obtained by wet-oxidizing an Al(Ga)As layer on the GaAs substrate [Reference 8], or the like can be attached to a gain medium grown on the InP substrate using wafer-to-wafer fusion method in order to fabricate an active device, such as a surface emitting laser.
[Reference 1]
Dennis G. Deppe, et al., Vertical cavity surface emitting lasers with electrically conducting mirrors, U.S. Pat. No. 5,068,868 (Nov. 26, 1991), AT&T Bell Laboratory.
[Reference 2]
Jamal Ramdani, et al., Long-wavelength light emitting vertical cavity surface emitting laser and method of fabrication, U.S. Pat. No. 6,121,068 (Sep. 19, 2000), Motorola, Inc.
[Reference 3]
Chao-Kun Lin, et al., Electrically pumped 1.3 μm VCSELs with InP/air-gap DBRs., Conference on Lasers and Electro-optics 2002, CPDB10-1, pp. 755˜757, 2002.
[Reference 4]
Chao-Kun Lin, et al., High temperature continuous-wave operation of 1.3–1.55 μm VCSELs with InP/air-gap DBRs, IEEE 18th International Semiconductor Laser Conference, ThA6, pp. 145˜146, 2002.
[Reference 5]
I. Sagnes, et al., MOCVD InP/AlGaInAs distributed Bragg reflector for 1.55 μm VCSELs, Electronics Letters, Vol. 37 (8), pp. 500˜501, 2001.
[Reference 6]
J. - H. Shin, et al., CW operation and threshold characteristics of all-monolithic InAlGaAs 1.55 μm VCSELs grown by MOCVD, IEEE Photonics Technology Letters, Vol. 14 (8), pp. 1031˜1033, 2002.
[Reference 7]
K. Streubel, et al., 1.26 μm vertical cavity laser with two InP/air-gap reflectors, Vol. 32 (15), pp. 1369˜1370, 1996.
[Reference 8]
H.- E. Shin, et al., High-finesse AlxOy/AlGaAs non-absorbing optical cavity, Applied Physics Letters, Vol. 72 (18), 1998.
[Reference 9]
Sun Jin Yun, et al., Dependence of atomic layer-deposited Al2O3 films characteristics on growth temperature and Al precursors of Al (CH3)3 and AlCl3., J. Vac. Sci. and Tech., vol 15 (6), pp. 2993˜2997, 1997.
[Reference 10]
Tuomo Suntola, et al., Method and equipment for growing thin films, U.S. Pat. No. 5,711,811 (Jan. 27, 1998).
[Reference 11]
Uchiyama Seiji, “surface light emitting semiconductor laser device and method for manufacturing thereof”, Japanese Patent Laid-Open No. H11-307863, Furukawa Electric Co. LTD.
[Reference 12]
Iwai Norihiro, et al., “surface emitting semiconductor laser device and its manufacture”, Japanese Patent Laid-Open No. H12-012962, Furukawa Electric Co. LTD.
However, the above-mentioned conventional semiconductor reflectors have the following advantages and disadvantages.
First, the InP/InAlAs reflector, the InAlGaAs/InAlAs reflector, the InAlGaAsSb/InAlAsSb reflector, and etc., which are obtained by the lattice-matched growth on the InP substrate, have an advantage that they are conductive reflectors [Reference 1] through which a current can be flowed. On the other hand, they have disadvantages that a growth thickness thereof is large and thickness adjustment or growth is difficult.
The InP/air-gap reflector, which can be obtained by the lattice matched growth on the InP substrate and the selective etch, has advantages that it has a small thickness and is easily fabricated while it has a disadvantage that it is mechanically weak and unstable.
In the case of dielectric reflector obtained by the deposition method and the Al(Ga)As/GaAs reflector grown on the GaAs substrate, and etc., a wafer-to-wafer fusion technique must be applied thereto. It is known that this technique has a disadvantage in mass production.
Further, in the case of the reflector obtained by growing crystalline thin films on the GaAs substrate and wet-oxidizing an Al(Ga)As layer of the grown crystal thin film, there is a problem of poor reliability due to the strain generated at the time of the wet-oxidizing.
Therefore, it is required to develop a semiconductor reflector and an optical filter that are able to overcome the disadvantages of the conventional semiconductor reflectors, and are more reliable in structure and easily fabricated.